1. Field
Aspects of the present invention relate to a secondary battery.
2. Description of the Related Art
Accidents, such as sparking or explosion that may occur in secondary batteries may foster a sense of insecurity in consumers and may lower reliability of the secondary battery. Further, many countries importing secondary batteries are tightening their regulations for safety tests.
In a safety test of a secondary battery, the secondary battery is subjected to an electrical test, such as a short circuit, abnormal charge, over-charge or forced discharge, and a stability test of a lithium ion battery against explosion or ignition in physically unstable conditions, such as vibration or impact.
In particular, in a longitudinal compression test among various safety tests of secondary batteries, stability due to deformation of the battery is tested by sharply compressing both sides of a battery can. When an electrode assembly of the battery is deformed during the longitudinal compression test, active materials of positive electrode plates are brought into direct contact with each other to cause an electrochemical reaction, resulting in an electric short. Accordingly, a probability of generating smoke and flames may increase, and there is a risk of explosion in the worst case.
In this regard, before an electrical short occurs due to contact between the active materials of the positive and negative electrode plates, a current discharge is caused to another battery element, thereby considerably reducing risks of ignition and explosion.
In general, the battery undergoes deformation when a can, and therefore other various battery elements, is compressed for the first time during the longitudinal compression test. Therefore, battery elements having different polarities are electrically short circuited to cause current drains, thereby considerably suppressing the risks of ignition and explosion of battery.
In order to easily distribute the force of an impact applied to the secondary battery during a drop weight impact test. In a conventional secondary battery, however, the size of the secondary battery is gradually diminished and a width of the can is gradually reduced so that battery elements having different polarities are often electrically short circuited during the drop weight impact test, thereby causing current drains.